The present invention relates to an improved oxidation catalyst and, more particularly, to a method for enhancing the catalytic activity of activated carbon for use in oxidation reactions.
U.S. Pat. No. 4,264,776 discloses and claims a process for preparing secondary amines by catalytic oxidation of tertiary amines with oxygen over carbon catalyst. The catalyst is an activated carbon of the type well known in the art and characterized by high absorptive capacity for gases, vapors, and colloidal solids and relatively high specific surface areas. Activation of commercially available carbon catalysts is usually achieved by heating the carbon to high temperatures (800.degree. C. to 900.degree. C.) with steam or with carbon dioxide which brings about a porous particulate structure and increased specific surface area.
U.S. Pat. No. 4,072,706 discloses a process for oxidative removal of phosphonomethyl groups from tertiary amines in which a molecular oxygen-containing gas is employed along with an activated carbon catalyst. It is noted that any source or form of carbon can be used as a catalyst or substrate in the process of the disclosed invention.
U.S. Pat. No. 3,969,398 teaches the use of activated carbon in the catalytic oxidation of N-(phosphonomethylimino)diacetic acid. It is stated that the carbon catalysts useful in the claimed process are available under a large number of trade names.
U.S. Pat. No. 3,497,564 discloses the use of amorphous or graphitic carbon as a catalyst in the oxidative dehydrogenation of alkylbenzenes. It is taught that activated carbon of whatever origin is operable in the process.
Japanese Patent application 56-17634 discloses an activation method for SO.sub.3 /SO.sub.2 conversion carbon materials which are useful as reduction catalysts to convert selectively SO.sub.3 in various gases, such as air and exhaust, to SO.sub.2. Carbon materials, such as cylindrical activated carbon, are treated with an oxidizing acid, e.g., nitric acid, followed by heat treatment at 300.degree. C. to 700.degree. C. under an inert gas.
U.S. Pat. No. 4,158,643 teaches a method for oxidative modification of an activated carbon support in which oxygen is added to the surface of the activated carbon, and then the carbon support is impregnated with an inert hydrophobic compound. The carbon support, which may be any commercially available activated carbon for vapor phase activation use, is useful in oxidizing carbon monoxide in the presence of sulfur dioxide for an extended period of time.
U.S. Pat. No. 3,243,383 teaches a method for regenerating spent catalysts which have been used for polymerizing olefins to liquid products. According to the disclosure, spent cobalt oxide on carbon catalyst is heated in an inert atmosphere, cooled, and then treated with nitric acid, nitric oxide, or nitrogen dioxide.
None of the foregoing references suggests that the surface of a carbon catalyst, particularly where acidic and basic surface oxides can be present, can play an important role in amine oxidation rates.